A semiconductor device preferably uses a substrate that getters metallic impurities in a manufacturing process thereof. For example, a silicon substrate with precipitation nuclei may getter metallic impurities, incorporating a metal element into the precipitation nucleus that contains oxygen, nitrogen, and boron that serves as a p-type impurity. There is also a method for gettering metallic impurities, using dislocations formed in a polysilicon layer provided on the backside of a silicon substrate. Further, a method is developed for forming a precipitation nucleus having a larger size and a higher density than the precipitation nucleus containing oxygen, nitrogen, and boron, using the carbon doping into a silicon crystal. Hence, it becomes possible, for example, to reduce white defects in an image sensor and to improve reliability of a gate dielectric film by increasing the gettering amount of metallic impurities.
According to the method using the carbon doping, no precipitation nucleus is formed while performing a crystal growth of silicon, and an initial nucleus is formed by a heat treatment at approximately 800° C. and enlarged by a heat treatment at 1000° C. or higher in wafer processing. That is, such heat treatments with high temperature are needed in the manufacturing process to form a precipitation nucleus containing carbon.
In recent years, the manufacturing process of a semiconductor device with an increasingly finer structure tends to limit a thermal budget in the wafer processing. For example, short-time heat treatment using RTA (Rapid Thermal Annealing) is preferably used, causing a precipitation nucleus to disappear and significant degradation in size and density of a precipitation nucleus. In addition, the application of transition metals such as titanium Ti, nickel Ni, and cobalt Co with a large diffusion coefficient at low temperature is broadening and raising the importance of gettering. Thus, a semiconductor device that improves the gettering of metallic impurities and a method of manufacturing such a semiconductor device are needed in a manufacturing process with the thermal budget limit.